1. Field of the Invention
The present invention relates to a photoresist composition containing a photo base generator (abbreviated as xe2x80x9cPBGxe2x80x9d). In particular, the invention relates to a photoresist composition comprising (a) a photoresist resin, (b) a photo acid generator, (c) an organic solvent and (d) a photo base generator. The photo base generator reduces or prevents sloping pattern and I/D Bias due to a higher concentration of acid in the upper portion of the photoresist relative to the concentration of acid in the lower portion of the photoresist.
2. Description of the Background Art
Use of chemical amplification-type photoresists (i.e., photoresist compositions) is currently being investigated in photolithography processes using light source such as KrF, ArF, VUV and EUV to achieve a high sensitivity in a minute image-formation on semiconductor devices. Such photoresist compositions are generally prepared by blending a photoacid generator with a matrix resin polymer (i.e., photoresist polymer or photoresist resin) having an acid labile group.
In a photolithography process, the resolution of an image depends on the wavelength of the light used. Thus, the shorter the wavelength, the higher the resolution, i.e., shorter wavelengths allow smaller pattern formation.
In order to be useful in a photolithography process, a photoresist composition must have an excellent etching resistance, heat resistance, and adhesiveness. Moreover, to reduce the cost of manufacturing semiconductor devices, a photoresist composition should be capable of being developed by a common developing solution, such as 2.38 wt % aqueous tetramethylammonium hydroxide (TMAH) solution. These qualities are particularly important in photolithography processes utilizing a deep ultraviolet light source (i.e., short wavelength light source), including KrF (248 nm), ArF (193 nm), VUV (157 nm) and EUV (13 nm).
However, it is very difficult to synthesize a photoresist composition that satisfies all of these requirements. For example, a photoresist polymer having a polyacrylate backbone is readily available, but it has poor etching resistance and is difficult to develop.
Etching resistance may be improved by adding alicyclic unit to the photoresist polymer; however, the presence of alicyclic unit in the photoresist polymer creates problems during the process for manufacturing semiconductor elements. For example, sloping pattern is formed when photoresist resin comprising the alicyclic units is used. Without being bound by any theory, it is believed that the sloping pattern formation is a result of having more light exposure on the upper portions of the PR composition relative to the lower portion of the PR composition (see FIG. 1). It is believed that the higher light exposure on the upper portions is due to an aerial image of the PR composition (or absorption of light by the resin). Other problems include a severe CD difference between isolated lines and dense lines (i.e., I/D bias) (see FIGS. 2 and 3).
The present inventors have found that when a PR composition is exposed to the same amount of light energy, there was more energy around the isolated lines of FIG. 2 than the dense lines of FIG. 3. Moreover, it was found that the acid concentration around the isolated lines was generally significantly higher than areas near the dense lines. This acid concentration gradient causes the acid to diffuse relatively easily resulting in narrower isolated lines relative to the dense lines when the PR composition is exposed to the same amount of light energy.
Therefore, there is a need for a photoresist composition which overcomes the above-mentioned disadvantages.
An object of the present invention is to provide photoresist compositions which significantly reduce or prevent the formation a sloping pattern (and hence a severe I/D bias occurrence) due to a higher concentration of generated acid in the upper portions of the photoresist composition relative to the lower portions of the photoresist composition.
Another object of the present invention is to provide a semiconductor element produced by using the Photoresist composition.